Solar cell module

ABSTRACT

A solar cell module includes a first solar cell including, in the following order, a single-crystalline silicon substrate, a conductive silicon layer, and a back side transparent electrode layer, where the conductive silicon layer and the back side transparent electrode layer are disposed on a back side of the single-crystalline silicon substrate; an encapsulant; and a flexible metal foil disposed between the back side transparent electrode layer and the encapsulant. The flexible metal foil is in contact with the back side transparent electrode layer in a non-bonded state. The encapsulant encapsulates the first solar cell and maintains a contact state between the flexible metal foil and the back side transparent electrode layer.

TECHNICAL FIELD

The present invention relates to a solar cell module including acrystalline silicon solar cell.

BACKGROUND ART

Crystalline silicon solar cells produced using a crystalline siliconsubstrate have high photoelectric conversion efficiency, and havealready been widely put into practical use as solar photovoltaic powergeneration systems. A crystalline silicon solar cell in which asilicon-based thin-film having a gap different from that ofsingle-crystalline silicon is disposed on a surface of asingle-crystalline silicon substrate to form a semiconductor junction iscalled a heterojunction solar cell, and exhibits particularly conversionefficiency among crystalline silicon solar cells.

In the crystalline silicon solar cell, carriers generated in acrystalline silicon are collected by a metal electrode disposed on thelight-receiving side and the back side. The heterojunction solar cellincludes a transparent electrode layer such as a transparent conductiveoxide (TCO) between a silicon-based thin-film and a metal electrode.Carriers collected by the metal electrode are extracted to outsidethrough a strip-shaped interconnector connected to the metal electrode.

Patent Document 1 discloses that when a metal plate or metal foil havinghigh rigidity onto a patterned metal electrode (Ag paste electrode) or atransparent electrode layer on the back side of a solar cell with aconductive adhesive interposed therebetween, damage by an external forceduring transportation, stress in an encapsulation process or the likecan be suppressed. Patent Document 2 discloses that when aninterconnector is connected to the back side of a solar cell, and theentire back surface is covered with a conductive sheet, seriesresistance can be reduced, and the thickness of the interconnector canbe reduced, so that warpage and breakage of the solar cell can besuppressed.

PRIOR ART DOCUMENT Patent Documents

-   Patent Document 1: Japanese Patent Laid-open Publication No.    2007-201331-   Patent Document 2: Japanese Patent Laid-open Publication No.    2005-167158

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

When a rigid member or a metallic member such as an interconnector ismounted on a light-receiving surface and a back surface of a crystallinesilicon solar cell with a conductive adhesive etc. interposedtherebetween, stress is generated at a bonding interface by heating inmodularization, a temperature change in practical use, or the like dueto, for example, a difference in thermal linear expansion coefficientbetween crystalline silicon and the metallic member. In a modulestructure as in Patent Document 1 and Patent Document 2, a metallicmember is bonded and mounted on each of both a light-receiving surfaceand a back surface of a solar cell, and therefore there is a differencebetween the magnitudes and directions of stress at the bonding interfaceon the front side and on the back side, so that warpage and breakage dueto strain of the cell, peeling of the metallic member, and so on easilyoccur. There is also the problem that use of a conductive adhesivecauses an increase in production cost.

An object of the present invention is to provide a solar cell module inwhich deterioration of properties, cell breakage, peeling of aninterconnector and so on due to a temperature change hardly occur, sothat excellent reliability is exhibited.

Means for Solving the Problems

A solar cell module according to the present invention includes a solarcell in which a conductive silicon layer and a back side transparentelectrode layer are disposed in this order on the back side of asingle-crystalline silicon substrate; an encapsulant; and a flexiblemetal foil disposed between the solar cell and the encapsulant. Themetal foil is in contact with the back side transparent electrode layerof the solar cell in a non-bonded state. The solar cell is encapsulatedby the encapsulant, and thus a contact state between the metal foil andthe back side transparent electrode layer is retained.

Preferably, at least a part of the metal foil which is in contact withthe back side transparent electrode layer includes at least one selectedfrom the group consisting of Sn, Ag, Ni, In, and Cu. The thickness ofthe metal foil is preferably 4 to 190 μm.

Preferably, the metal foil is provided with a plurality of openings, andthe encapsulant is in contact with the solar cell through the openings.The diameter of the opening provided in the metal foil is preferably 100μm to 2000 μm, and the distance between openings closest to each otheris preferably 5 mm to 100 mm.

On the back side transparent electrode layer of the solar cell, aplurality of dot-shaped buffer electrodes may exist separately from oneanother. On a surface of the solar cell on the back side, the area of aregion occupied by the buffer electrodes is preferably less than 1% ofthe area of a region in which the back side transparent electrode layeris exposed. When dot-shaped buffer electrodes are disposed on the backsurface of the solar cell, it is preferable that the metal foil is incontact with the back side transparent electrode layer and the bufferelectrodes in a non-bonded state, and is electrically connected to theback side transparent electrode layer and the buffer electrodes.

When the solar cell includes a patterned metal electrode on thelight-receiving surface, back electrodes and light-receiving side metalelectrodes in two adjacent solar cells are electrically connected toperform interconnection. In two adjacent solar cells, a metal foil thatis in contact with a back side transparent electrode in one solar cell(“first solar cell”) and a metal electrode on a light-receiving surfaceof the other solar cell (“second cell”) are mounted to a connectionmember to electrically connect the two adjacent solar cells.

Solar cells may be interconnected using a wiring sheet with a metal foilfixed on an insulating member. When the metal foil is provided with aplurality of openings, it is preferable that the insulating member hasopening sections at positions corresponding to the openings of the metalfoil. In this embodiment, it is preferable that the encapsulant is incontact with the solar cell through the opening sections provided in theinsulating member and the openings provided in the metal foil. Thediameter of the opening section of the insulating member is preferablysmaller than the diameter of the opening provided in the metal foil.

Effects of the Invention

In a solar cell module according to the present invention,interconnection is performed through a metal foil that is in contactwith the back side of a solar cell in a non-bonded state, and thereforeeven when a temperature change occurs, stress strain is hardlygenerated, so that excellent temperature reliability is exhibited. Theuse amount of the metal electrode material on the back side is reduced,resulting in contribution to cost reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing one embodiment of a solar cellmodule.

FIG. 2 is a schematic view showing one embodiment of a solar cell.

FIG. 3A is a plan view showing one examples of a pattern of thelight-receiving side metal electrode.

FIG. 3B is a plan view showing one examples of a pattern of thelight-receiving side metal electrode.

FIG. 4 is a conceptual view showing a state in which a metal foil is incontact with a back surface of a solar cell in a non-bonded state.

FIG. 5 is a plan view of a solar cell having buffer electrodes.

FIG. 6 shows a cross-section of a solar cell module including a solarcell having buffer electrodes.

FIG. 7 is a sectional view of a solar cell module including a metal foilprovided with openings.

FIG. 8A is a plan view of a light-receiving surface of a solar cellmodule.

FIG. 8B is a plan view of a back surface of a solar cell module.

FIG. 9 is a conceptual view illustrating a state in which light iscaptured from a back surface of a solar cell.

FIG. 10A is a plan view of a wiring sheet to be used for interconnectionof solar cells.

FIG. 10B is a sectional view of a wiring sheet to be used forinterconnection of solar cells.

FIG. 11 is a sectional view showing a state in which solar cells aredisposed on a wiring sheet.

FIG. 12A is a plan view of solar cell strings connected by a wiringsheet.

FIG. 12B is a plan view of solar cell strings connected by a wiringsheet.

FIG. 13 is a schematic view showing one embodiment of a solar cellmodule.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic view showing a solar cell module structureaccording to one embodiment of the present invention. A solar cellmodule (hereinafter, sometimes referred to as a “module”) has aconfiguration in which a solar cell (hereinafter, sometimes referred toas a “cell”) is encapsulated by an encapsulant. The module shown in FIG.1 includes a light-receiving surface protecting member 10, alight-receiving side encapsulant 11, a connection member 12, a cell 13,a metal foil 14, a back side encapsulant 16 and a back sheet 17 in thisorder from the light-receiving side.

For encapsulants 11 and 16, a resin such as EVA (ethylene vinyl acetate)or a polyolefin is used. The resin is heated and melted, and fluidized,so that the encapsulant flows between adjacent cells and to edges of themodule to perform modularization.

The light-receiving surface protecting member 10 disposed on thelight-receiving side of a cell include is light-transmissive, andexamples of the material thereof include glass substrates (blue glasssubstrates and white glass substrates), and organic films such asfluororesin films such as polyvinyl fluoride films (e.g., TEDLAR FILM(registered trademark)), and polyethylene terephthalate (PET) films.From the viewpoint of mechanical strength, light transmittance, moistureresistance reliability, costs and so on, white glass substrates areespecially preferable.

The back sheet 17 disposed on the back side of the cell may have any oflight-transmissivity, light-absorbency and light-reflectivity. As theback sheet having light-transmissivity, one described above as amaterial of the light-receiving surface protecting material ispreferably used. As the back sheet having light-reflectivity, one havinga metallic color or white color is preferable, and a white resin film, alaminate with a metal foil of aluminum etc. sandwiched between resinfilms, or the like is preferably used. As the back sheet havinglight-absorbency, for example, one including a black resin layer isused.

On the back side of the cell 13, the metal foil 14 is disposed betweenthe cell 13 and the back side encapsulant 16. The metal foil 14 is incontact with the back surface of the cell 13 in a non-bonded state, andis thus electrically connected to the cell. Before modularization, thecell 13 and the metal foil 14 are in detachable contact with each other.In the module, the cell is encapsulated by the encapsulant to retain acontact state between the metal foil and the cell.

FIG. 2 shows a schematic view of a cross-section of a crystallinesilicon solar cell. A crystalline silicon solar cell 13 includes a backside conductive silicon layer 7 and a back side transparent electrodelayer 8 on the back side of a single-crystalline silicon substrate 5.Preferably, a back side intrinsic silicon layer 6 is provided betweenthe single-crystalline silicon substrate 5 and back side conductivesilicon layer 7.

Preferably, a light-receiving side intrinsic silicon layer 4, alight-receiving side conductive silicon layer 3 and a light-receivingside transparent electrode layer 2 are formed on the light-receivingside of the single-crystalline silicon substrate 5. The light-receivingside conductive silicon layer 3 has a conductivity-type opposite to thatof the back side conductive silicon layer 7. Thus, one of thelight-receiving side conductive silicon layer 3 and the back sideconductive silicon layer 7 is p-type, and the other is n-type. Theconductivity-type of the single-crystalline silicon substrate 5 may beeither p-type or n-type. It is preferable to use an n-typesingle-crystalline silicon substrate from the viewpoint of a lifetime.

Preferably, fine irregularity (texture) structures having a height ofabout 2 to 10 μm are formed on a surface of the single-crystallinesilicon substrate 5. Pyramidal irregularity structure whose surfaces arecomposed of (111) plane can be formed on the single-crystalline siliconsubstrate by anisotropic etching. Preferably, irregularity structuresare formed on both the light-receiving surface and the back surface ofthe solar cell.

In the solar cell shown in FIG. 2, a metal electrode is not disposed onthe back side transparent electrode layer 8. On the light-receiving sidetransparent electrode layer 2, a patterned metal electrode is disposedas a light-receiving side electrode 1. The light-receiving side metalelectrode 1 acts to transport a current in the in-plane direction of thelight-receiving surface of the cell 13, and therefore thelight-receiving side metal electrode 1 has a two-dimensional pattern inthe in-plane direction of the light-receiving surface. Examples of thetwo-dimensional pattern in the in-plane direction include a shape inwhich a plurality of finger electrodes 111 extending in parallel asshown in FIG. 3A, and a grid shape pattern including finger electrodes111 and bus bar electrodes 112 orthogonal to the finger electrodes asshown in FIG. 3B. When the light-receiving side metal electrode 1includes only finger electrodes as shown in FIG. 3A, a connection memberis disposed so as to extend across a plurality of finger electrodes inthe module. When a grid shape light-receiving side metal electrodehaving bus bar electrode as shown in FIG. 3B is provided, a connectionmember is disposed on the bus bar electrode 112.

The flexible metal foil 14 is disposed on the back surface of the cell13. In the module, the metal foil 14 and the back side transparentelectrode layer 8 of the cell are in contact with each other in anon-bonded state. In this specification, the state in which the metalfoil and the back side transparent electrode layer (and the bufferelectrode) are “contact . . . in a non-bonded state” means a state inwhich the metal foil and the back side transparent electrode layer arebrought into contact with each other by applying a physical externalforce such as pressing or suction. Accordingly, in the state beforeencapsulation is performed using the encapsulant, the metal foil and thecell are in detachable contact with each other. A state in which themetal foil and the back side transparent electrode are bonded to eachother by an adhesive, a molten solder or the like, and a state in whicha metal electrode is formed on the transparent electrode layer byprinting, plating, sputtering or the like do not correspond to the“contact . . . in a non-bonded state”

The metal foil 14 may be partially fixed on the back surface of the cellwith a conductive adhesive material such as a conductive film, solder orconductive paste or an insulating adhesive material such as a pressuresensitive adhesive tape interposed therebetween. The partial fixation istemporary tacking for fixing the positional relationship between thecell 13 and the metal foil 14, and is not intended to adhesively stackthe cell 13 and the metal foil 14 together. Thus, when the metal foil ispartially fixed on the back surface of the cell, the metal foil and thecell are in contact with each other in a non-bonded state at portionsother than temporary stacking portions. When the metal foil is partiallyfixed on the back surface of the cell, there may be one temporarystacking portion. For suppressing such a failure that the metal foil isturned up during operation such as encapsulation, it is preferable toperform temporary stacking at two or more portions. As described indetail later, a metal foil may be fixed on an insulating support basematerial. In this case, temporary tacking of the cell to the metal foilis unnecessary, so that operability in modularization can be improved.

As a material of the metal foil 14, one having low contact resistancewith the back side transparent electrode layer, or a sort metal ispreferably used. The metal having low contact resistance is preferablyAg, Ni, Au or the like, and the sort metal is preferably Sn, Cu, In, Alor the like. The metal foil 14 may be a single layer, or may have aplurality of stacked metal layers. When the metal foil is a singlelayer, it is preferable to use a metal foil including at least one metalselected from the group consisting of Sn, Ag, Ni, In, and Cu. Inparticular, it is preferable to use a copper foil as the metal foil 14because it has a high reflectance and is inexpensive. For the metal foilin which a plurality of metal layers are stacked, it is preferable thata metal layer including at least one selected from the group consistingof Sn, Ag, Ni, In, and Cu is used for the contact surface with the backside transparent electrode layer. For example, a metal foil in which alow-contact resistance metal layer of Ag or the like as a contact layerwith the back side transparent electrode layer is provided on a copperfoil surface may be used.

The thickness of the metal foil 14 is preferably 4 to 190 μm, morepreferably 10 to 100 μm, especially preferably 15 to 50 μm. When thethickness of the metal foil is 4 μm or more, an increase in electricresistance of the metal foil itself can be suppressed. When thethickness is 190 μm or less, a local increase in resistance can besuppressed because the metal foil has flexibility, and can follow thesurface shape of the cell. By using a metal foil including a material asdescribed above and having a thickness within the above-mentioned range,uniform contact with the back side transparent electrode layer, andmoderate strength and flexibility of the metal foil can be secured.

In the module in FIG. 1, a space between the light-receiving surfaceprotecting member 10 and the back sheet 17 is filled with encapsulants11 and 16. By performing encapsulation with the metal foil 14 disposedon the back surface of the cell 13, a contact state between the backside transparent electrode layer and the metal foil is retained. Byfixing the metal foil by an external force from the encapsulant, themetal foil and the back side transparent electrode layer can be broughtinto uniform contact with each other. Since the cell and the metal foilare in a non-bonded state, stress at the interface is relaxed. Thus,deterioration of properties due to cell breakage and strain issuppressed, so that a module having high reliability is obtained.

In a state in which the metal foil and the transparent electrode are incontact with each other, void portions may exist on a part of thesurface of the back side between the metal foil and the transparentelectrode. FIG. 4 is an enlarged view of the back side of a module inwhich the metal foil 14 is in contact, in a non-bonded state, with thetop of the back side transparent electrode layer 8 of the cell 13 havingirregularities on the back surface of a silicon substrate.

When irregularity structures are formed on the back side of the cell,peak portions (projections) of the irregularity structures come intocontact with the metal foil to establish electrical contact. When theback side transparent electrode layer on the peaks of irregularitystructures and periphery thereof are brought into contact with the metalfoil, it is preferable that the irregularity size is small, and thenumber of peaks per area (pea density) is large.

When the back surface of the cell has irregularity structures, a regionsurrounded by the back side transparent electrode layer 8 and the metalfoil 14 is not filled with an encapsulant, and thus forms a void. Thevoid portion 18 is filled with a gas (air) before encapsulation, and isin a state close to vacuum after encapsulation. After encapsulation, thevoid portion 18 is in a negative pressure state, and therefore a contactstate between the metal foil 14 and the back side transparent electrodelayer 8 is retained.

Single-crystalline silicon has a small light absorption coefficient fornear infrared light, and therefore, of light incident to the cell fromthe light-receiving surface, most of light having a long wavelength of950 nm or more reaches the back side without being absorbed in thesingle-crystalline silicon substrate. Since the refractive index of ametal oxide material that forms the transparent electrode layer is about2 while the refractive index of the void portion is about 1 to 1.05, apart of light reaching the back surface of the cell is reflected at theinterface between the back side transparent electrode layer and thevoid, and is incident to the silicon substrate again. Remained part ofthe light reaching the back surface of the cell passes through theinterface between the back side transparent electrode layer, and is thenreflected at the interface between the void and the metal film, passesthrough the interface between the back side transparent electrode layerand the void again, and is incident to the cell again.

Preferably, a void portion exists between the transparent electrode andthe metal foil in a region occupying 80% or more and less than 100% ofthe projected area of a surface of the back side transparent electrode.In particular, for securing conductivity with the metal foil whilesecuring a maximum reflectance on the back side, it is preferable that avoid portion exists in a region occupying 85% or more and less than 100%of the projected area of the surface of the back side transparentelectrode, and it is especially preferable that a void portion exists ina region occupying 90% or more and less than 100% of the projected areaof the surface of the back side transparent electrode.

The “surface of back side transparent electrode” means a region in whichthe back side transparent electrode is exposed in a state before it isbrought into contact with the metal foil. Thus, it is preferable thatthe void portion occupies 80% or more and less than 100% of the region,and the other region, i.e., a region occupying more than 0% and 20% orless of the aforementioned region, is in contact with the metal foil.When metal electrodes such as dot-shaped buffer electrodes are providedon the back side transparent electrode as described later, a regionwhich is not provided with the metal electrodes corresponds to the“surface of back side transparent electrode”.

As one of the effects of this embodiment, plasmon absorption at theinterface between the back side transparent electrode and the metalelectrode does not occur because the metal electrode is not formeddirectly on the back side transparent electrode.

Generally, in a heterojunction solar cell, the thickness of the backside transparent electrode layer is set to 80 to 100 nm to maximizereflection at the interface between silicon and the back sidetransparent electrode layer for reducing plasmon absorption at theinterface between the back side transparent electrode layer and themetal electrode. On the other hand, when a metal foil as the back sidemetal electrode is brought into physical contact with the back side,plasmon absorption at the interface between the back side transparentelectrode layer and the metal electrode can be suppressed toconsiderably reduce the thickness of the back side transparent electrodelayer to about 20 nm. By reducing the thickness of the back sidetransparent electrode layer, absorption of light by the back sidetransparent electrode layer is reduced, and therefore light utilizationefficiency can be further improved.

When the thickness of the back side transparent electrode layer issmall, mechanical damage to the peaks of irregularities tends to easilyoccur. Dot-shaped buffer electrodes 9 may be provided on the back sidetransparent electrode layer 8 for suppressing mechanical damage to thecell. FIG. 5 is an enlarged view of the back surface of the cellprovided with dot-shaped buffer electrodes. As described above, thelight-receiving side metal electrode 1 is two-dimensionally providedwhile extending in at least one direction in the plane, whereas bufferelectrodes 9 provided on the back surface is not required to have afunction of transporting a current in the in-plane direction of the backsurface. Thus, as shown in FIG. 5, a plurality of buffer electrodes 9exist separately from one another. When the metal foil 14 comes intocontact with the back side transparent electrode layer 8 and the bufferelectrode 9, the back side transparent electrode layer is electricallyconnected to a plurality of buffer electrodes through the metal foil.

FIG. 6 shows a schematic cross-section of a module including a cell withthe buffer electrode 9 provided on the back side transparent electrodelayer 8. When the buffer electrode 9 is disposed, the buffer electrode 9and the metal foil 14 first come into contact with each other inapplication of a pressure, and the metal foil 14 is pressed onto theback side transparent electrode layer 8 where the buffer electrode 9does not exist. First the buffer electrode 9 receives a pressure fromthe metal foil 14, and therefore the contact pressure between the backside transparent electrode layer 8 and the metal foil 14 in the regionwhich is not provided with the buffer electrode 9 is equalized. Thus,local application of a pressure to the back side transparent electrodelayer 8 is suppressed, so that mechanical damage can be reduced.

On a surface of the cell on the back side, the area of a region providedwith the buffer electrode 9 is preferably less than 1% of the area of aregion in which the back side transparent electrode layer 8 is exposed.Thus, the ratio A2/A1 is preferably less than 0.01 where A1 is the areaof a region in which the back side transparent electrode layer 8 isexposed, and A2 is the total area of dot-shaped buffer electrodes. Theratio A2/A1 is more preferably 0.002 to 0.007. When the bufferelectrode-formed area is within the above-mentioned range, low contactresistance and moderate pressure dispersion can be expected. As comparedto a case where a grid shape metal electrode is formed, the use amountof electrode materials such as an Ag paste is smaller, and therefore theproduction cost can be reduced.

The height of the buffer electrode is preferably larger than the heightof irregularities on the back surface of the cell. The height of thebuffer electrode is preferably about 6 to 30 μm. The height of thebuffer electrode 9 is more preferably about 10 to 25 μm from theviewpoint of a balance between reduction of the material cost and thebuffering ability. The diameter of the buffer electrode is preferablyabout 10 to 100 μm, and more preferably about 30 to 60 μm from theviewpoint of utilization efficiency of materials and uniformity ofpatterning. The distance d between buffer electrodes closest to eachother is preferably about 0.5 to 3 mm. When the size of the bufferelectrode and the distance between the buffer electrodes are within theabove-mentioned ranges, respectively, mechanical damage tends to bereduced, leading to suppression of a reduction in open circuit voltage(Voc) which is associated with modularization. Due to equalization ofthe pressure, contact resistance is equalized, series resistancedecreases, and the fill factor (FF) of the module tends to be improved.

As a material of the buffer electrode, for example, a paste obtained bymixing fine particles formed of a material such as Sn, Ag, Ni, Al, Cu orcarbon and a binder such as epoxy or PVDF can be used, and it ispreferable to use fine particles formed of at least one of Sn, Ag and Nifrom the viewpoint of pressure relaxation and contact resistance. Thebuffer electrodes can be formed by, for example, screen printing.

The metal foil 14 may be provided with an opening. When the metal foil14 is provided with an opening 141 as shown in FIG. 7, the back sideencapsulant 16 flows to the back surface of the cell 13 through theopening 141, and therefore adhesion can be improved. An encapsulant 165may flow into gaps between the metal foil 14 and the back sidetransparent electrode layer 8 (or buffer electrode 9) as the encapsulant16 flows not only to just above the opening 141 but also to theperiphery of the opening 141.

The diameter of the opening 141 of the metal foil 14 is preferably 100to 2000 μm, more preferably 200 to 1500 μm, further preferably 400 to900 μm. When the diameter of the opening is 100 μm or more, theencapsulant 16 can easily pass through the opening, so that adhesionwith the cell is improved. When the diameter of the opening is 2000 μmor less, the encapsulant 16 is prevented from excessively flowing intogaps between the metal foil 14 and the cell 13, so that the contact areabetween the metal foil and the back surface of the cell can bemaintained.

The distance between openings closest to each other is preferably 5 to100 mm, more preferably 6 to 26 mm. When the distance between theopenings is within the above-mentioned range, the contact area betweenthe metal foil 14 and the back side transparent electrode layer 8 andbuffer electrode 9 can be secured while adhesion between the encapsulant16 and the cell 13 on the back side is kept appropriately.

As described above, the metal foil 14 disposed in contact with the backsurface of the cell 13 serves as a metal electrode that feeds a currentin the in-plane direction of the back surface of the solar cell. Themetal foil 14 can be used for interconnection between adjacent cells.

In the module shown in FIG. 1, the connection member (interconnector) 12such as a tab line is mounted on the light-receiving side metalelectrode 1. The light-receiving side metal electrode 1 and theconnection member 12 can be electrically connected through solder, aconductive adhesive, a conductive film or the like. One end of theconnection member 12 mounted on the light-receiving side metal electrodeis mounted on the metal foil 14 disposed in contact with the adjacentcell.

FIG. 8A is a plan view of a light-receiving surface of a solar cellmodule in which the connection member 12 mounted on the light-receivingside metal electrode 1 is connected to a projected portion 149 of themetal foil 14 disposed in contact with the adjacent cell. FIG. 8B is aplan view of a back surface of the module.

Cells 131 and 132 included in this module each have a rectangular shapeor a substantially rectangular shape in a plan view. The substantiallyrectangular shape is a shape of a rectangle, the corners of which arechamfered. The substantially rectangular shape is also referred to as asemi-square shape. The metal foil 14 that is in contact with the backsurface of one cell 131, of two adjacent cells 131 and 132, is disposedso as to have the projected portion 149 in which the metal foilprotrudes to the other cell 132 side. When the connection member 12connected to the light-receiving surface of the cell 132 is connected tothe projected portion 149 of the metal foil 14 that is in contact withthe back surface of the cell 131, the two cells are electricallyconnected.

When an interconnector composed of a metal having a thermal expansioncoefficient different from that of the silicon substrate is fixed to thecell with solder, an adhesive or the like interposed therebetween,stress is generated at the bonding interface due to a temperature changeetc. When an interconnector is mounted on each of both surfaces of thecell, there is a difference between the magnitudes and directions ofstress on the front side and on the back side, so that strain may beeasily generated, leading to reduction of Voc due to strain, peeling ofthe interconnector, cell breakage due to stress, and so on.

On the other hand, in the embodiment shown in FIGS. 8A and 8B, only themetal foil 14 is in contact with the back side of the cell in anon-bonded state, and a bonding member is not used. Thus, deteriorationof module characteristics due to a temperature change hardly occurs, sothat excellent reliability is exhibited. Since it is not necessary toconnect an interconnector to the back surface of the cell, cellinterconnection operation can be simplified to improve productivity ofthe module.

It is preferable that on three sides other than a side on which theprojected portion 149 of the metal foil exists, among the four sides ofthe rectangular or substantially rectangular cell, the metal foil 14 isdisposed inside the peripheral edge of the cell, and the cell is exposedat an end portion which is not covered with the metal foil. Thus, it ispreferable that the peripheral edge of the metal foil exists inside theperipheral edge of the cell except for the projected portion 149 forestablishing connection to the adjacent cell.

When an exposed portion which is not provided with the metal foil 14exists on the peripheral portion of the back surface of the cell, lightLA incident to a gap between adjacent cells followed by reflection atthe back sheet 17 can be caused to pass into the cell from the exposedportion of the back surface of the cell as schematically shown in FIG.9, so that light utilization efficiency of the module is improved. Thewidth W of the exposed portion of the back surface of the cell ispreferably about 0.3 to 2 mm, more preferably about 0.5 to 1.5 mm.

A plurality of cells are interconnected to form a solar cell string,encapsulation is performed with an encapsulant disposed on each of bothsurfaces of the solar cell string, whereby the cells are modularized. Ininterconnection, alignment of each cell and metal foil is performed, andrelative alignment of a plurality of cells is performed.

By using a wiring sheet 150 with a plurality of metal foils fixed on aninsulating support, alignment operation can be simplified. FIG. 10A is aplan view of the wiring sheet 150 with the metal foil 14 fixed on asheet-shaped insulating member 15, and FIG. 10B is a sectional viewtaken along line A1-A2. FIG. 11 is a plan view showing a state in whicha cell is placed on a surface of a metal foil on a side opposite to asurface fixed with an insulating member, the metal foil being fixed to awiring sheet. FIG. 12A is a plan view showing a state in whichlight-receiving side metal electrodes (bus bar electrodes) and metalfoils in two adjacent cells are interconnected by the connection member12. FIG. 12B is a sectional view taken along line B1-B2. FIG. 13 is aschematic sectional view of a module in which cells are interconnectedusing a wiring sheet.

The material and the thickness of the insulating member 15 are notparticularly limited as long as it is capable of supporting the metalfoil, and has heat resistance at a lamination temperature (e.g., 120 to150° C.) in encapsulation. The insulating member 15 may have any oflight-transmissivity, light-absorbency and light-reflectivity. When alight-reflective back sheet is used, it is preferable that theinsulating member 15 has light-transmissivity. As the insulating member15, a PET (polyethylene terephthalate) resin sheet is preferably usedfrom the viewpoint of transparency and the material cost.

A plurality of metal foils 14 matching the number of cells included inone module are fixed on the insulating member 15. For example, in FIG.10A, nine (3×3) metal foils 14 are disposed separately from one anotheron one insulating member 15. The method for fixing the insulating member15 and the metal foil 14 to each other is not particularly limited, andthe metal foil can be fixed by, for example, static electricity, anadhesive, welding or the like. Particularly, it is preferable that themetal foil is fixed on the insulating member by a low-adhesion pressuresensitive adhesive.

When the metal foil 14 is provided with a plurality of openings 141 asshown in FIG. 10A, it is preferable that the insulating member 15 hasfirst-kind opening sections 151 at positions corresponding to theopenings of the metal foil. The “position corresponding to the openingof the metal foil” means a position at which the opening is provided inthe metal foil that is in contact with the back surface of the cell. Inthe module after encapsulation, the back sheet 17, the back sideencapsulant 16, the insulating member 15, the metal foil 14 and the cell13 are disposed in this order from the back side as shown in FIG. 13.When first-kind opening sections 151 of the insulating member 15 areprovided at positions corresponding to openings 141 of the metal foil14, the back side encapsulant 16 flows to the back surface of the cell13 through first-kind opening sections 151 of the insulating member 15and openings 141 of the metal foil 14, and therefore adhesion can beimproved.

The diameter of the first-kind opening section 151 provided in theinsulating member 15 is preferably smaller than the diameter of theopening 141 of the metal foil 14. When the opening of the metal foil islarger than the opening section of the insulating member, the pressureof inflow of the encapsulant is relaxed at the opening of the metalfoil. Thus, the encapsulant 16 is inhibited from excessively flowinginto gaps between the metal foil 14 and the cell 13, so that the contactarea between the metal foil and the back surface of the cell can bemaintained. In a region where openings are provided in the metal foil,and first-kind opening sections are not provided in the insulatingmember, the back surface of the cell 13 and the insulating member 15 arebonded to each other with the encapsulant 16 interposed therebetween.Accordingly, the metal foil 14 is sandwiched and fixed between theinsulating member and the cell, so that the cell 13 and the metal foil14 can be brought into contact with each other more reliably. Thediameter of the first-kind opening section 151 of the insulating member15 is more preferably about 30 to 80%, further preferably 30 to 60%, ofthe diameter of the opening 141 of the metal foil 14. The diameter ofthe first-kind opening section 151 is preferably 270 to 1000 μm, morepreferably 300 to 700 μm.

Preferably, the insulating member 15 has second-kind opening sections inregions where the metal foil 14 is not disposed, i.e., second-kindopening sections 152 at positions corresponding to gaps between adjacentcells (see FIG. 13). Since opening sections are provided at positionscorresponding to gaps between adjacent cells, the encapsulant easilyflows not only to the back surface of the cell, but also to the lateralsurface of the cell and a gap between cells, so that encapsulation canbe more reliably performed. The diameter of the second-kind openingsection 152 of the insulating member 15 provided in a region where themetal foil is not disposed is preferably 270 to 1000 μm, more preferably300 to 700 μm.

As shown in FIG. 11, cells are disposed on metal foils 14 on a wiringsheet. By this operation, alignment of the cell 13 and the metal foil14, and relative alignment of a plurality of cells are performedsimultaneously. Thus, alignment operation can be simplified to improveproductivity of the module.

In FIG. 11, the cell is not disposed on the metal foil 14 at a portionin which the cell is interconnected to the adjacent cell. Thus, the cell13 is disposed in such a manner that the metal foil 14 has the projectedportion 149 protruding from the cell-disposed region.

The connection member 12 is mounted on the light-receiving side metalelectrode 1 of the cell 13 and the projected portion 149 of the metalfoil 14 to form a solar cell string in which a plurality of cells areconnected in series as shown in FIGS. 12A and 12B. In FIG. 12A, threesolar cell strings each having three cells connected in the x directionare arranged in the y direction, and adjacent solar cell strings areconnected by a lead wire 22. To a cell at an end portion is connected alead wire 21 for extracting a current to outside.

As shown in FIG. 12B, the connection member 12 is mounted on the bus barelectrode 112 of the light-receiving surface. As described above, theconnection member 12 and the bus bar electrode 112 (light-receiving sidemetal electrode) can be electrically connected using solder, aconductive adhesive, a conductive film or the like. For electricalconnection of the connection member 12 and the bus bar electrode 112,solder, a conductive adhesive, a conductive film or the like can beused. For facilitating connection operation, it is preferable to connectthe metal foil and the connection member by a method to identical to themethod for connecting the light-receiving side metal electrode and theconnection member. For example, when the light-receiving side metalelectrode 1 and the connection member 12 are soldered to each other, itis preferable to connect the metal foil 14 and the connection member 12by soldering. In FIG. 12B, a solder-welded portion 125 is formed at aconnection portion (interconnection portion) with the connection memberon the metal foil 14.

When interconnection is performed with the connection member 12 mountedonto the metal foil 14 by soldering etc., the insulating member may bemelted or deformed by heating. Particularly, when a resin film of PET orthe like is used as an insulating member, the insulating member iseasily melted or deformed because the heating temperature duringinterconnection exceeds the heat-resistant temperature of the insulatingmember. For preventing a failure caused by heat during interconnection,it is preferable that in the insulating member 15, third-kind openingsections 153 are provided in regions including positions correspondingto interconnection portions, i.e., at positions corresponding toportions where the metal foil 14 and the connection member 12 overlapeach other, and on the periphery thereof.

When third-kind opening sections 153 are provided at interconnectionportions and on the periphery thereof, melding or deformation of theinsulating member due to elevation of the temperature of the insulatingmember during interconnection can be prevented. When the insulatingmember 15 is provided with third-kind opening sections, soldering or thelike can be performed by heating from the back side through thethird-kind opening sections. When opening sections 153 are provided, itis easy to re-solder a connection failure portion even if the connectionfailure portion is generated in interconnection by heating from thelight-receiving side.

The size of the third-kind opening section of the insulating member isnot particularly limited, but the opening is preferably larger than theinterconnection portion. Preferably, the third-kind opening section 153is provided so as to extend over a region in which the metal foil 14 isdisposed and a region in which the metal foil is not disposed. Althoughcircular third-kind opening sections are shown in FIGS. 10 to 12, theshape of the third-kind opening section is not limited to a circularshape. For example, the third-kind opening section may be provided so asto extend in a direction (y direction) orthogonal to the interconnectiondirection along the end portion of a region provided with the metal foil(projected portion of the metal foil).

After a plurality of cells are connected on a wiring sheet to form asolar cell string, an encapsulant and a protecting member are disposedand stacked on the light-receiving side and the back side, respectively,of the solar cell string, and heated and press-bonded, whereby theencapsulant flows between cells and to the edges of the module toperform encapsulation. When the insulating member 15 and the metal foil14 are provided with openings, the encapsulant flows to the back surfaceof the cell 13 through the opening as shown in FIG. 12. Thus, the celland the encapsulant come into close contact with each other to suppressingress of moisture etc. Thus, a solar cell module having highreliability is obtained.

EXAMPLES

Hereinafter, the present invention will be described in detail byshowing examples, but the present invention is not limited to thefollowing examples.

[Preparation of Heterojunction Solar Cell]

A 200 μm-thick 6 inch n-type single-crystalline silicon substrate havingan incident surface with a (100) plane orientation was washed inacetone, immersed in a 2 wt % HF aqueous solution for 5 minutes toremove a silicon oxide layer on a surface, and rinsed twice withultra-pure water. Thus obtained substrate was immersed for 15 minutes ina 5/15 wt % KOH/isopropyl alcohol aqueous solution held at 75° C.Thereafter, the substrate was immersed in a 2 wt % HF aqueous solutionfor 5 minutes, rinsed twice with ultra-pure water, and dried at normaltemperature. The surfaces of the single-crystalline silicon substratewere observed with an atomic force microscope (AFM). Quadrangularpyramid-like textured structures were formed on both surfaces and thearithmetic mean roughness thereof was 2100 nm.

The texture-formed single-crystalline silicon substrate was introducedinto a CVD apparatus, and a 4 nm-thick i-type amorphous silicon layerwas formed as a light-receiving side intrinsic silicon layer on thelight-receiving surface. On the i-type amorphous silicon layer, a 5nm-thick p-type amorphous silicon layer was formed as a light-receivingside conductive silicon layer. Deposition conditions of thelight-receiving side intrinsic silicon layer were the followings: thesubstrate temperature was 180° C.; the pressure was 130 Pa; the SiH₄/H₂flow rate ratio was 2/10; and the input power density was 0.03 W/cm².Deposition conditions of p-type amorphous silicon layer were thefollowings: the substrate temperature was 190° C.; the pressure was 130Pa; the SiH₄/H₂/B₂H₆ flow ratio was 1/10/3; and the input power densitywas 0.04 W/cm². As the B₂H₆ gas mentioned above, a gas diluted with H₂to a B₂H₆ concentration of 5000 ppm was used.

The substrate was transferred to a sputtering chamber without beingexposed to air. On the p-type amorphous silicon layer, a 120 nm-thickITO layer was formed as a light-receiving side transparent electrode. Asa sputtering target, one obtained by adding 10% by weight of SnO₂ toIn₂O₃ was used.

The substrate with the ITO layer deposited on the light-receivingsurface was reversed, and introduced into a CVD apparatus, and a 5nm-thick i-type amorphous silicon layer was deposited on the backsurface of the silicon substrate as a back side intrinsic silicon layer.A 10 nm-thick n-type amorphous silicon layer was deposited thereon as aback side conductive silicon layer. Deposition conditions of the n-typeamorphous silicon layer were the followings: the substrate temperaturewas 180° C., the pressure was 60 Pa, the SiH₄/PH₃ flow rate ratio was1/2, and the input power density was 0.02 W/cm². As the PH₃ gas, a gasdiluted with H₂ to a PH₃ concentration of 5000 ppm was used.

Next, the substrate was transferred to a sputtering chamber withoutbeing exposed to atmospheric air, and a 100 nm-thick ITO layer wasdeposited on the n-type amorphous silicon layer as a back sidetransparent electrode layer.

In the following examples and comparative examples, a solar cell wasprepared using the solar cell in process, which was obtained asdescribed above, and a plurality of solar cells were connected throughan interconnector to modularize the solar cells.

Example 1

(Formation of Metal Electrode)

On an ITO layer on a light-receiving surface, a silver paste wasscreen-printed to form a grid shape light-receiving side metal electrodeincluding finger electrodes and bus bar electrodes as shown in FIG. 3B.A metal electrode was not disposed on an ITO layer on a back surface,and a solar cell was formed in such a manner that a back sidetransparent electrode layer is an outermost surface layer.

(Interconnection)

A metal foil (36 μm-thick copper foil) was cut into a rectangular shape,and brought into contact with the ITO layer on the back surface of thesolar cell. The metal foil was disposed in such a manner that aprojected portion exposed outside the end portion of a cell existed on aside where the cell was interconnected to the adjacent cell, and an endportion of the metal was situated 0.5 mm inside the end portion of thesolar cell on the other three sides.

For interconnection of adjacent cells, a connection member obtained bycovering a 1.5 mm-wide and 200 μm-thick strip-shaped copper foil withsolder was used. Three connection members disposed at equal intervalswere abutted against bus bar electrodes on the light-receiving surfaceand the projected portion of the metal foil disposed in contact with theback surface of the adjacent cell, and a soldering iron heated to 360°C. was pressed thereto, whereby adjacent cells were electricallyconnected to form a solar cell string with nine solar cells connected inseries. Six solar cell strings (54 solar cells in total) were connectedin series to prepare a string assembly.

(Encapsulation)

A 4 mm-thick white glass plate as a light-receiving surface protectingmember, a 400 μm-thick EVA sheet as each of a light-receiving sideencapsulant and a back side encapsulant, and a PET film as a back sheetwere provided, the string assembly was sandwiched between the two EVAsheets, and lamination was performed at 150° C. for 20 minutes to obtaina solar cell module.

Example 2

(Formation of Metal Electrode)

In the same manner as in Example 1, a grid shape metal electrode wasformed on an ITO layer on a light-receiving surface. Further, dot-shapedmetal electrodes (buffer electrodes) each having a diameter of 30 to 70μm were formed on an ITO layer on a back surface by screen printing. Thedot-shaped metal electrodes were disposed at intervals of 1 mm in atriangular grid shape.

(Interconnection and Encapsulation)

In the same manner as in Example 1, a metal foil was disposed on theback surface of each of solar cells, the solar cells were interconnectedto prepare a string assembly, and encapsulation was performed. Across-section of the module after encapsulation was examined, and theresult showed that the metal foil was deformed in the disposition cycleof buffer electrodes. In a region within 200 μm to 300 μm from theperiphery of the buffer electrode, the metal foil was not in contactwith a back side transparent electrode layer, and in a region moredistant from the periphery of the buffer electrode, the metal foil wasin physical contact with the back side transparent electrode layer.

Example 3

A wiring sheet obtained by arranging 54 (9×6) metal foils on a PET filmand bonding the metal foils to the PET film was used. In the PET filmand the metal foils of the wiring sheet, openings were provided atintervals of 25 mm in a square grid shape in regions where the PET filmand the metal foil overlapped each other. The diameter of each of theopenings provided in the PET film and the metal foil was 300 μm A cellwith dot-shaped buffer electrodes provided on the back surface in thesame manner as in Example 2 was disposed on the wiring sheet, and aconnection member was soldered to bus bar electrodes on thelight-receiving surface and projected portions of the metal foils toperform interconnection.

Example 4

A wiring sheet with metal foils having openings each having a diameterof 800 μm was used. A solar cell module was prepared in the same manneras in Example 3 except for the above.

Example 5

In Example 5, a PET film of a wiring member had opening sections notonly in regions where the metal foil was disposed, but also atconnection portions (interconnection portions) between a connectionmember and the metal foil, and in regions of gaps between cells wherethe metal foil was not provided. The opening sections at theinterconnection portion were provided so as to surround theinterconnection portion, and openings reached outside the end portion ofa region where the metal foil was disposed. Interconnection wasperformed by soldering a connection member to the metal foil disposed onthe opening sections (see FIG. 13). A solar cell module was prepared inthe same manner as in Example 4 except for the above.

Example 6

A metal foil cut to a size larger than that in Example 1. The metal foilwas disposed so as to protrude about 0.5 mm outside the end portion ofthe cell on three sides other than a side involved in interconnection tothe adjacent cell. A solar cell module was prepared in the same manneras in Example 1 except for the above.

Comparative Example 1

In the same manner as in Example 1, a grid shape metal electrode wasformed on an ITO layer on a light-receiving surface. Further, a gridshape metal electrode was formed on an ITO layer on a back surface. Thenumber of bus bar electrodes on the back side was 3 and equal to thenumber of bus bar electrodes on the light-receiving side, and the numberof finger electrodes on the back side was three times as large as thenumber of finger electrodes on the light-receiving side. The metal foilwas disposed in contact with the back surface of a solar cell, and thebus bar electrodes of a back side grid electrode and a metal foil werebonded using a conductive adhesive, and fixed together. A solar cellmodule was prepared in the same manner as in Example 1 except for theabove.

Comparative Example 2

In the same manner as in Comparative Example 1, a grid shape metalelectrode was formed on each of both a light-receiving surface and aback surface. Bus bar electrodes on the back surface and a metal foilwere bonded using an epoxy-based insulating adhesive in place of theconductive adhesive in Comparative Example 1. The whole surface of themetal foil at portions other than projected portions was coated with theepoxy-based adhesive, and press-bonded to the back surface of the solarcell in a heated state at about 150 to 160° C. to bond metal electrodesto the metal foil. In this example, metal electrodes (bus bar electrodesand finger electrodes) having a projected structure with respect to aback side transparent electrode layer break through an epoxy resin layerin press-bonding, and the epoxy resin is cured with the metal electrodesbeing in contact with the metal foil, so that the metal electrodes arebonded to the metal foil in a contact state.

Comparative Example 3

In the same manner as in Comparative Example 1, a grid shape metalelectrode was formed on each of both a light-receiving surface and aback surface. Bus bars on the light-receiving surface and bus bars onthe back surface of the adjacent cell were soldered and connected to aconnection member to electrically connect adjacent cells without using ametal foil. A solar cell module was prepared in the same manner as inComparative Example 1 except for the above.

Comparative Example 4

Except that a back side transparent electrode layer was bonded to ametal foil with a conductive adhesive, the same procedure as in Example1 was carried out to prepare a solar cell module.

Comparative Example 5

As in Example 2, dot-shaped buffer electrodes were formed on a back sidetransparent electrode layer, and except that the back side transparentelectrode layer and buffer electrodes were bonded to a metal foil with aconductive adhesive, the same procedure as in Example 2 was carried outto prepare a solar cell module.

[Evaluation]

The initial power generation characteristics of the solar cell module ineach of Examples and Comparative Examples were measured, and atemperature cycle test was then conducted in accordance with JIS C8917.The solar cell module was introduced into a test bath, and thensubjected to a temperature cycle test including 200 cycles. Each cycleincludes a process in which the solar cell module is held at 85° C. for10 minutes, cooled to −40° C. at a rate of 80° C./minute, held at −40°C. for 10 minutes, and heated to 85° C. at a rate of 80° C./minute. Thepower generation of the solar cell module after the temperature cycletest was measured, and the ratio of the power after the temperaturecycle test to the initial power (retention) in the solar cell module wasdetermined. The configuration of the solar cell module, the initialpower generation characteristics, and the retention after thetemperature cycle test are shown in Table 1.

TABLE 1 Metal foil Position of end portion Inside or Distance Insulatingmember Back Connection Diameter outside of from Diameter Initial stageside to back of peripheral peripheral of Series metal Presence/ surfaceopening edge edge of cell Presence/ opening resistance Power electrodeabsence of cell (μm) of cell (mm) absence (μm) (Ω) (W) Retention Example1 None Present Non-bonded — Inside 0.5 — — 0.346 273.2 96.30% contactExample 2 Dot Present Non-bonded — Inside 0.5 — — 0.313 274.5 96.89%contact Example 3 Dot Present Non-bonded 300 Inside 0.5 Present 3000.330 274.2 97.52% contact Example 4 Dot Present Non-bonded 800 Inside0.5 Present 300 0.325 274.3 97.91% contact Example 5 Dot PresentNon-bonded 800 Inside 0.5 Present 300 0.322 274.9 98.02% contact Example6 None Present Non-bonded — Outside 0.5 — — 0.342 272.5 96.40% contactComparative Grid Present Conductive — Inside 0.5 — — 0.359 269.8 93.29%Example 1 adhesive Comparative Grid Present Insulating — Inside 0.5 — —0.464 259.8 95.47% Example 2 adhesive Comparative Grid — Solder- —Inside 0.5 — — 0.357 272.8 96.25% Example 3 connection between bus barand connection member Comparative None Present Conductive — Inside 0.5 —— 0.379 269.1 93.50% Example 4 adhesive Comparative Dot PresentConductive — Inside 0.5 — — 0.358 270.3 93.80% Example 5 adhesive

Examples 1 to 5 showed a higher initial power and retention after thecycle test as compared to Comparative Example 3 in which metalelectrodes on the front and back sides were connected by a connectionmember without using a metal member. The reason why the initial powerwas improved in Examples 1 to 5 may be that existence of voids betweenthe metal foil and the back side transparent electrode improved thereflectance, leading to an increase in current. Further, it isconsidered that the back electrode of the cell and the metal foil werein contact with each other in a non-bonded state, and therefore evenwhen dimensions were changed due to a temperature change, stress was notgenerated at the interface between the cell and the metal foil, anddeterioration of characteristics resulting from stress strain etc. wassuppressed, resulting in improvement of the retention after the cycletest.

Comparative Examples 1 and 2 in which the metal foil and the back sidegrid electrode were bonded using an adhesive had a lower initial powerand retention after the temperature cycle test as compared toComparative Example 3. It is considered that in Comparative Example 1,absorption of light by a conductive adhesive caused reduction of theinitial power. In Comparative Example 2, series resistance increased,and the fill factor decreased. This may be because the contact areabetween the back side grid electrode and the metal foil decreased due tointerposition of an insulating adhesive.

In Comparative Examples 1 and 2, series resistance increased after thecycle test although these data are not shown in Table 1. This may bebecause since a metal foil and a solar cell having mutually differentthermal expansion coefficients were bonded by an adhesive, stress at theinterface was not relaxed, and thus peeling occurred locally.

Among Examples, Examples 3 to 5 showed a high retention after the cycletest. This may be because through openings provided the metal foil andthe insulating member, the encapsulant was bonded to the back sidetransparent electrode layer to suppress displacement of the metal foildue to thermal expansion during the temperature cycle test.

Particularly, Examples 4 and 5 showed a high retention. This may berelated to the fact that the diameter of the opening of the metal foilis larger than the diameter of the opening of the insulating member.When the opening of the metal foil is larger than the opening of theinsulating layer, a region having an insulating member under theopenings of the metal foil (region where the insulating member is notprovided with openings) exists. Thus, an encapsulant can be interposedbetween the insulating member and the back side metal electrode layer,and the metal foil sandwiched between the insulating member and the backside transparent electrode layer is fixed by the encapsulant, so thatdisplacement is suppressed. This may be one cause of the high retentionin Examples 4 and 5. Thus, it is considered that in Examples 4 and 5,the retention after the cycle test was improved because due tointerposition of the encapsulant, the cell and the metal foil were incontact with each other in a non-bonded state while the relativepositions of the cell and the metal foil were fixed.

Example 6 in which a metal foil larger in size than the cell was usedshowed a slightly lower initial power as compared to Example 1. This isbecause of light reflected in the module, light reflected at the backsheet to reach the end portion of the cell was blocked off by the metalfoil, so that the light was unable to pass into the cell, and thereforethe current value decreased. It is considered that in Examples 1 to 5,since the end portion of the metal foil was situated at the inside ofthe cell at portions other than projected portions for interconnection,light was efficiently recovered, so that the current value relativelyincreased, leading to improvement of the power generation.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   1 light-receiving side metal electrode    -   2 light-receiving side transparent electrode    -   3 light-receiving side conductive silicon layer    -   4 light-receiving side intrinsic silicon layer    -   5 single-crystalline silicon substrate    -   6 back side intrinsic silicon layer    -   7 back side conductive silicon layer    -   8 back side transparent electrode layer    -   9 buffer electrode    -   10 light-receiving surface protecting member    -   11 light-receiving side encapsulant    -   12 connection member    -   13 solar cell    -   14 metal foil        -   141 opening    -   15 insulating member        -   151, 152, 153 opening    -   16 back side encapsulant    -   17 back sheet

What is claimed is:
 1. A solar cell module comprising: a first solarcell comprising, in the following order, a single-crystalline siliconsubstrate, a conductive silicon layer, and a back side transparentelectrode layer, wherein the conductive silicon layer and the back sidetransparent electrode layer are disposed on a back side of thesingle-crystalline silicon substrate; an encapsulant; and a flexiblemetal foil disposed between the back side transparent electrode layerand the encapsulant, wherein the flexible metal foil is in contact withthe back side transparent electrode layer in a non-bonded state, and theencapsulant encapsulates the first solar cell and maintains a contactstate between the flexible metal foil and the back side transparentelectrode layer.
 2. The solar cell module according to claim 1, whereinat least a part of the flexible metal foil is composed of at least oneselected from the group consisting of Sn, Ag, Ni, In, and Cu.
 3. Thesolar cell module according to claim 1, wherein a thickness of theflexible metal foil is 4 to 190 μm.
 4. The solar cell module accordingto claim 1, wherein a plurality of dot-shaped buffer electrodes aredisposed on the back side transparent electrode layer separately fromone another, and wherein the flexible metal foil is in contact with thebuffer electrodes in a non-bonded state, and is electrically connectedto the back side transparent electrode layer and the buffer electrodes.5. The solar cell module according to claim 4, wherein on a back surfaceof the first solar cell, an area of a region occupied by the bufferelectrodes is less than 1% of an area of a region in which the back sidetransparent electrode layer is exposed.
 6. The solar cell moduleaccording to claim 1, wherein the flexible metal foil is provided with aplurality of openings, and the encapsulant is in contact with the firstsolar cell through the openings.
 7. The solar cell module according toclaim 6, wherein a diameter of the opening is 100 μm to 2000 μm, and adistance between the openings closest to each other is 5 mm to 100 mm.8. The solar cell module according to claim 1, wherein the flexiblemetal foil is fixed on an insulating member, and the back sidetransparent electrode layer is in contact in a non-bonded state with asurface of the flexible metal foil on a side opposite to a surface fixedwith the insulating member.
 9. The solar cell module according to claim8, wherein the flexible metal foil is provided with a plurality ofopenings, the insulating member has first opening sections at positionscorresponding to the openings of the flexible metal foil, and theencapsulant is in contact with a back surface of the first solar cellthrough the first opening sections provided in the insulating member andthe openings provided in the flexible metal foil.
 10. The solar cellmodule according to claim 9, wherein a diameter of the first openingsection is smaller than a diameter of the opening provided in theflexible metal foil.
 11. The solar cell module according to claim 8,wherein the insulating member has second opening sections in a regionwhere the flexible metal foil is not disposed, and the encapsulant is incontact with a lateral surface of the first solar cell through thesecond opening sections provided in the insulating member.
 12. The solarcell module according to claim 1, further comprising a second solar celladjacent to the first solar cell, wherein the second solar cellcomprises a patterned metal electrode on a light-receiving surfacethereof, and the flexible metal foil that is in contact with the backside transparent electrode in the first solar cell and the metalelectrode of the second solar cell are mounted to a connection member toelectrically connect the two adjacent solar cells.
 13. The solar cellmodule according to claim 12, wherein the flexible metal foil that is incontact with the back side transparent electrode of the first solar cellhas a projected portion protruding from a peripheral edge of the firstsolar cell, and the connection member is mounted on the projectedportion of the flexible metal foil.
 14. The solar cell module accordingto claim 13, wherein the first and second solar cells have a rectangularshape or a substantially rectangular shape in a plan view, the projectedportion of the flexible metal foil is arranged on a side of the firstsolar cell which is adjacent to the second solar cell, and the flexiblemetal foil is disposed inside three peripheral edges of the first solarcell.
 15. The solar cell module according to claim 13, wherein theflexible metal foil is fixed on an insulating member, and the back sidetransparent electrode layer is in contact in a non-bonded state with asurface of the flexible metal foil on a side opposite to a surface fixedwith the insulating member, and the insulating member has third openingsections in a region including positions corresponding to connectionportions between the projected portion of the flexible metal foil andthe connection member.